At the end of the comment, you are right.

Maxwell equations (electromagnetism) depend on the charge of the (anti)particle. Therefore, the same equations are used regardless of the matter/antimatter nature of the particle. In some equation, you will have a +e and in other a -e, that's it. Magnetism stays the same (the same laws are used). From the same laws, we will derive the magnetic field (and its direction will be different).